The head of the civil service officially reprimanded David Cameron over the behaviour of his special advisers following 'unacceptable' briefings to journalists, PR Week has learned.

Sir Gus O'Donnell was so alarmed at briefings coming out of Government that he wrote a strongly worded letter to the Prime Minister urging him to restrain his aides.

The Cabinet Secretary was provoked into taking the unprecedented action by newspaper reports concerning Jenny Watson, a former Audit Commission board member.

O’Donnell is said to have been furious after The Times quoted a Whitehall source describing Watson as ‘incompetent’ and revealing she had been removed from her role.

The letter from the Cabinet Secretary to the PM is understood to have read: ‘You will have been aware of briefings to the media regarding Jenny Watson. This behaviour is unacceptable. I trust you will agree with me and take necessary action to make sure that people understand this will not be tolerated.’

In response to a Freedom of Information request by PRWeek, the Cabinet Office confirmed that O’Donnell had written to the PM in late 2010 to discuss ‘the role, status or conduct of government special advisers’. However, an official declined to provide the correspondence in question.

A spokesman for the Cabinet Office said: ‘We never comment on any advice the Cabinet Secretary might or might not have provided to the Prime Minister.’

But a Downing Street insider who witnessed the episode unfolding spoke of mounting concern in Whitehall about the activities of some Tory special advisers. The source said: ‘The quotes about Jenny Watson were the final straw. Gus was so concerned that he raised it with the PM a few days later, saying this is unacceptable behaviour and please rein in your spads.’

The insider said that Cameron had been expected to admonish a special adviser, but Downing Street told PRWeek there were no records of the PM meeting with the relevant advisers to discuss their conduct.

The controversial quotes first appeared in The Times on 8 September 2010. The newspaper had reported that Communities Secretary Eric Pickles was embarking on ‘a bonfire of the quangocrats’ with Watson top of the hit list. The contempt of Pickles for many quango executives was reflected in a sweeping statement about Watson, attributed to a Whitehall source.

The source told the Times: ‘She was begging Mr Pickles to stay on but we are not having someone who built their career on incompetence continuing to milk the taxpayer.

‘She is not fit for the role. The Audit Commission has lost its way and the last thing we need is someone like her on board. She has no previous experience outside the public sector. We have had a bonfire of the quangos; now we are having a bonfire of the quangocrats.’

In response to a Freedom of Information request by PRWeek, a Cabinet Office official confirmed that the cabinet secretary had written to the PM or his chief of staff in the wake of the report. The request had asked for ‘any letters, emails or faxes sent by Sir Gus O’Donnell to the Prime Minister or Edward Llewellyn concerning the role, status or conduct of government special advisers’ in September and October 2010.

The official wrote back: ‘I can confirm the Cabinet Office holds some information related to your request on the role, status or conduct of government special advisers.’

However, the official declined to provide the correspondence in question, claiming that disclosure would contravene the first data protection principle, which provides that personal data must be processed fairly and lawfully. The official also stonewalled repeated requests to provide a redacted version of the correspondence.

Last night, the official said: ‘We are still considering your request.’

Responding to a separate Freedom of Information request, Downing Street said it had no records of any meetings the PM had held with Pickles’ special advisers to discuss their conduct in September 2010.